The present invention relates in general to a gas sensor and a gas sensor unit using the gas sensor.
Conventionally, a limiting-type current gas sensor was used for detecting concentration of oxygen and steam in a measurement gas. The limiting-type current gas sensor is provided with a cathode and an anode. Each of the cathode and the anode is formed on a solid electrolyte for conducting oxygen ion, and is composed of a porous electrode. The cathode of the limiting-type current gas sensor is provided with a gas diffusion control which is composed of a cover having a small hole, or composed of a porous body. With the thus provided gas diffusion control, the gas diffusion moving from a measurement atmosphere toward the cathode can be controlled. For example, when a gas in the measurement atmosphere contains oxygen, the oxygen is sent to the cathode through the gas diffusion control. At this point in time, if a proper voltage is applied between the cathode and the anode, the oxygen that is dissociated on the cathode is ionized and then is flowed toward the anode in the solid electrolyte. The current caused by the ionized oxygen is called a pumping current. The thus obtained pumping current is saturated at the limiting current value, which is obtained when diffusion rate of the oxygen passing through the gas diffusion control reaches a controlled value. It is known that the limiting current value is substantially proportional to the oxygen concentration in the gas.
In this case, what is measurable is not limited to the concentration of molecular oxygen. For example, concentration of water (steam) is also measurable in the following manner, provided that the water (steam) contains oxygen atom in its molecule: Increase the voltage between the anode and the cathode to such an extent that an electrolysis of the molecular water (steam) is caused, to thereby cause the limiting current. With the thus obtained limiting current, the concentration of the water (steam) is measurable. This summarizes that the limiting-type current gas sensor is not limited to measurement of oxygen concentration. More specifically, the limiting-type current gas sensor is also used for measuring steam concentration (or partial pressure) in an exhaust gas from general purpose internal combustion engines such as boiler and the like. However, no art is provided or even proposed that is capable of measuring atmospheric pressure, altitude and the like by means of such gas sensor.
It is, therefore, an object of the present invention to provide a gas sensor that is capable of detecting pressure of a measurement gas.
It is another object of the present invention to provide a sensor unit that is capable of outputting pieces of information on an atmospheric pressure, altitude and the like by means of the gas sensor.
There is provided a gas sensor, according to the present invention. The gas sensor comprises: a sensor element formed of a solid electrolyte having an oxygen ion conductivity; a cathode and an anode, each formed of a porous metal material and each formed on the sensor element, to produce a pumping current reflecting a concentration of a detection component in a measurement gas when a predetermined voltage is applied between the cathode and the anode, the detection component comprising oxygen, the measurement gas contacting the cathode; and a gas diffusion control to vary the oxygen pumping current in accordance with a pressure of the measurement gas by controlling a diffusion of the measurement gas, the measurement gas moving from a measurement atmosphere toward the cathode by way of the gas diffusion control, to thereby obtain information on the pressure of the measurement gas based on the oxygen pumping current.
Moreover, there is provided a sensor unit, according to the present invention. The sensor unit comprises a pressure sensor. The pressure sensor comprises: a sensor element formed of a solid electrolyte having an oxygen ion conductivity; a cathode and an anode, each formed of a porous metal material and each formed on the sensor element, to produce a pumping current reflecting a concentration of a detection component in a measurement gas when a predetermined voltage is applied between the cathode and the anode, the detection component comprising oxygen, the measurement gas contacting the cathode; and a gas diffusion control to vary the oxygen pumping current in accordance with a pressure of the measurement gas by controlling a diffusion of the measurement gas, the measurement gas moving from a measurement atmosphere toward the cathode by way of the gas diffusion control, to thereby obtain information on the pressure of the measurement gas based on the oxygen pumping current. The sensor unit generates and outputs information on an atmospheric pressure and an altitude based on the information on the pressure obtained by the pressure sensor.